1. Field of the Invention
The present invention relates to a linear array ultrasonic transducer used in an ultrasonic diagnostic examination device, and more particularly to such a transducer in which an ultrasonic beam is projected into an object to be examined, such as a living body, to receive the echoes which are reflected from the boundary between heterogenous bodies having different acoustic impedances.
2. Description of the Prior Art
The construction of and the problems concomitant with a transducer according to the prior art will now be described.
Referring to FIG. 1 which is a perspective view showing an oscillatory array portion of a transducer, the transducer includes an oscillatory element 1a which is made of a material such as PZT (i.e., piezoelectric element of Lead Zirconate-Titanate). Electrode layers 1b and 1c are provided on both sides of the oscillatory element 1a. Oscillatory element 1a thus formed with the electrode layers 1b and 1c usually is a member of a large plate-shaped oscillator. This part of the plate-shaped oscillator is adhered to a backing member, which will be described later, and is then cut thin into an array form, as shown in FIG. 1. The single thin cut element from the oscillatory element 1a is indicated as a tiny oscillatory element 11. A backing member 2 absorbs the ultrasonic waves directed to the back of the array of the tiny oscillatory elements 11.
In order to clearly produce the image which is obtained by the ultrasonic diagnostic examination device using such a transducer, a variety of means have been employed, including such means relating to the transducer as follows:
(1) The oscillatory frequency of the ultrasonic waves is increased; PA1 (2) A side lobe is reduced in the directive characteristics of the ultrasonic beam; and PA1 (3) The ultrasonic beam is made thin and sharp.
As has been described above, such means involved the construction of the tiny oscillatory elements having a rectangular shape which are made thinner.
The operation of the transducer shown in FIG. 1 is as follows. For example, five tiny oscillatory elements 11 are gathered into one group, and the electrode layers of any of the tiny oscillatory elements are denoted a.sub.K and b.sub.K, the electrode layers a.sub.1 to a.sub.5 and b.sub.1 to b.sub.5 are electrically connected (although the respective tiny oscillatory elements are acoustically insulated), and a pulsed voltage signal is applied between the electrode layers a.sub.1 to a.sub.5 and b.sub.1 to b.sub.5 so that one ultrasonic beam is transmitted from that group of the tiny oscillatory elements. A number of such groups are arranged in an array to transmit the ultrasonic beam consecutively, thereby to effect the scanning operation.
FIG. 2 is a perspective view showing one tiny oscillatory element. In order to realize the aforementioned means (2), if the thickness and width of the tiny oscillatory element are denoted as t and W, respectively, as is disclosed in May, 1977 "Proceedings of Japanese Ultrasonic Medical Association", page 53, the ratio of W/t is desired to be equal to or less than 0.6. For example, therefore, in order to generate ultrasonic waves having a frequency of 5 MHz, the thickness t of the tiny oscillatory element has to be about 0.25 mm, and the width W has to be about 0.15 mm.
Electrode leads for driving such tiny oscillatory elements, according to the prior art, have been attached to the electrode layers 1b and 1c by a bonding process. This bonding process involves bonding the leads one by one to the tiny oscillatory elements (generally, about three hundred in number having a width of 0.15 mm) which required skilled working techniques and is time consuming. As a result, the bonding process has been an intrinsic cause for the failure of the apparatus in which the array is incorporated. It has been extremely difficult to complete the bonding of the tiny oscillatory elements as many as three hundred times without any failure occurring.